Variable displacement engines may employ a valve deactivation assembly including a rolling finger follower that is switchable from an activated mode to a deactivated mode. One method for activating and deactivating the rocking arm includes an oil-pressure actuated latch pin within the inner arm of the rolling finger follower. In a first mode, the pin engages the inner arm and outer arm in a latched condition to actuate motion of the outer arm, thereby moving a poppet valve that controls one of the intake or exhaust of gases in the combustion chamber. In a second mode, the inner arm is disengaged from the outer arm in an unlatched condition, and the motion of the inner arm is not translated to the poppet valve.
Mode transitions, either from the latched condition to the unlatched condition, or vice versa, may be designed to occur only when the cam is on the base circle portion. For example, mode transitions may be controlled to occur only when the roller follower is engaging the base circle portion of the cam. This ensures that the mode change occurs while the valve deactivator assembly, and more specifically the latching mechanism, is not under a load.
Due to the high rotational speed of a cam, it may be difficult to reduce the amount of time needed to transition from a latched condition to an unlatched condition in order to execute the transition during a single base circle period. The inventors have recognized that one problematic issue that may arise during mode transitions in a rolling finger follower with an oil-pressure actuated latch pin is the presence of air within the latch pin circuit, which is compressible and increases the amount of time needed to switch from the latched condition to the unlatched condition or vice versa.
Other attempts to address entrapped air within the deactivation circuit include air expansion chambers. One example approach is shown by Hendriksma in U.S. Pat. No. 8,662,035. Therein, a pressure differential within the hydraulic circuit is utilized to flow the entrapped air through first and second flow constriction region of an oil bypass passage. By configuring the second flow constriction region to be less constricting than the first, the first and second flow constriction regions establish a pressure differential therebetween. Air may expand in the volume between each constriction region at a reduced rate by means of the pressure differential, thereby reducing pressure oscillations within the hydraulic circuit caused by a more rapid expansion of air.
However, the inventors herein have recognized potential issues with such systems. As one example, particulate matter within the oil may accumulate at one or more of the flow constriction regions. The particulate matter may degrade the constricting of the oil, and may thereby reducing the reliability of the pressure differential established between the flow constriction regions. Thus, the reduction of pressure oscillations may become less reliable.
Other attempts to address the accumulation of particulate matter at a flow constriction region include a combined restrictor/filter to insert within a lifter oil manifold assembly. One example approach is shown by Borraccia et al. in U.S. Pat. No. 7,946,262. Therein, an unrestricted oil pump feed flows through a combined restrictor/filter to supply a restricted amount of oil to the deactivatable valve lifters of the engine. The combined restrictor/filter is configured to rest atop a dam that directs the flow through a filter, an internal passageway, and a restriction orifice of the restrictor/filter.
However, the inventors herein have recognized potential issues with such systems. As one example, even with a sealant, leakage may still occur at the interface of the dam and the restrictor/filter, thereby bypassing the restriction orifice and creating unpredictable pressures downstream of the restriction orifice. Additionally, if filter degradation is present, the entire restrictor/filter unit may need to be replaced, introducing high maintenance costs.
In one example, the issues described above may be addressed by a hydraulic circuit for a poppet valve deactivation mechanism of an engine, comprising a poppet valve deactivation control valve including an outlet that is in communication with first and second oil galleries, the galleries also each in communication with a DHLA, and a hydraulic flow restriction hydraulically in series between the first and second galleries, said hydraulic flow restriction including a restricted horizontal groove in a camshaft carrier that fluidly couples a first vertical bore to a second vertical bore.
As one example, the first and second oil galleries may be in communication with a dual-function hydraulic lash adjuster. During activated cylinder conditions, pressure in the first oil gallery may be greater than in the second oil gallery, and oil may flow from the first gallery to the second gallery via the restricted horizontal groove. The hydraulic flow restriction may be machined into a bottom face of a camshaft carrier. The direction of flow during the activated cylinder conditions may be such that any air in the second gallery flows with the restricted flow of oil toward a pressure relief valve in a valve deactivation oil control valve. Each vertical bore may include an interchangeable oil filter to reduce the amount of particulate matter within the oil before the oil flows through the restrictive groove. In this way, the amount of air within the hydraulic circuit may be reliably reduced, and the degradation of the restrictor of the deactivation circuit due to accumulated particulate matter may also be reduced. Additionally, by machining the hydraulic flow restrictor into the bottom of the camshaft carrier, leakage and packing constraints may be reduced.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.